Communication systems having both uplink and downlink capabilities are typically characterized by a number of constraints. First, in such a communication system, uplink and downlink transmissions use different frequencies but are typically simultaneous. Downlink and uplink transmissions are also centrally scheduled frame-by-frame by a central controller, also referred to as an Access Point (AP). Such communication systems also provide support for half duplex terminals, and half duplex terminals are allowed to transmit before receiving and/or vice-versa. A half-duplex terminal is a terminal that alternates between sending and receiving information. An example of such a system is the air interface for the Institute of Electrical and Electronics Engineers (IEEE) 802.16 fixed broadband wireless access system.
When half duplex terminals are used in a particular communication system, the bandwidth controller does not allocate uplink bandwidth to a half-duplex terminal at the same time that it is expected to receive data on the downlink channel, including allowance for the propagation delay, the terminal transmit/receive transition gap and the terminal receive/transmit transition gap. On the other hand, the bandwidth controller may have to determine which packets should be the next to be transmitted, i.e. how to allocate bandwidth, in order to meet a variety of system-defined requirements. These requirements may include, for example, the provisioning of quality of service (“QoS”) considerations.